The present invention relates to apparatus and methods for stabilizing and maintaining adjacent bone portions in predetermined desired relationships and constraining one, two or three-dimensional motion and/or rotation of the adjacent bone portions. More particularly, the present invention relates to a magnetic apparatus with at least two magnetic arrays, each of which may include at least one magnet arranged in a predetermined manner and each magnetic array generating a magnetic field therearound. Once implanted and secured to the adjacent bone portions, the magnetic apparatus provides interacting magnetic fields in the area of the bone portions and transduces magnetic energy into mechanical energy and mechanical energy into potential magnetic energy, thereby reproducing functionally anatomic and/or anatomically advantageous arrangement of the bone portions.
Orthopedics is a medical subspecialty that treats disorders of the human body related to bones, muscles, ligaments, tendons, and joints, with its current emphasis on the treatment of the bones and joints. The treatment of bone and joint disorders can be generally subclassified into categories including the treatment of bone fractures, joint instability, early stage arthritis, and end stage arthritis. Originally, the treatment of orthopedic conditions had mainly relied on casting and bracing. However, with the advent of new implantable materials and development of better joint replacement prostheses, orthopedics shifted its focus to become increasingly more of a surgical subspecialty. With improved materials, better engineering, and a better understanding of the human body, the practice of orthopedic medicine and biomechanical experimentation have made remarkable progress. The treatment of bone fractures and joint disorders has continually been refined to the present state-of-the-art. The last 40 years have shown a myriad of innovations that have concentrated specifically on developing static mechanical design characteristics and new implantable materials used for fracture treatment and in total joint arthroplasties. These static mechanical design characteristics have been directed to solutions for problems concerning wear, stability, and methods of fixation for the total joint arthroplasties. They have also been utilized to improve the current state of the art concerning fracture treatment.
There have been some attempts to develop applications that utilize nonmechanical forces to augment the treatment of particular orthopedic problems. For example, pulsating electromagnetic field has been used as an adjunct to stimulating bone healing. Biochemical and biomaterial means have been used to alter the milieu at fracture sites and in joints to aid healing and to decelerate disease processes. Others have attempted to utilize magnetic fields in treatment of bone and joint disorders as well. For example, U.S. Pat. No. 4,024,588 to Janssen, et al. describes artificial joints with magnets. U.S. Pat. No. 4,029,091 to Von Bezold et al. discloses a method of applying plates to fractured bones so as to allow limited motions of the bone fragments when subjected to an externally generated electromagnetic force. U.S. Pat. No. 4,322,037 to Esformes et al. suggests a elbow joint including mechanically interlocking joint components with the inclusion of a magnetic force on the joint. U.S. Pat. No. 5,595,563 to Moisdon discloses a method of repositioning body parts through magnetic induction generated by extracorporeal magnetic or electromagnetic devices. U.S. Pat. No. 5,879,386 to Jore describes an apparatus to hold bones apart which can also be adjustable from inside the joint, possibly through arthroscopic means. The disclosed devices and methods had only limited uses for specific orthopedic problems. However, these designs are generally not practically feasible due to errors or misconceptions related to the practical application of orthopedic surgical treatments or, more importantly, a lack of understanding concerning the properties of permanent magnets in relationship to the mechanical environment found in the human body, especially as they relate to the normal functions of bones and joints. Accordingly, there remains a need in the art for improved apparatus and methods for less invasively locating and restraining bones in treatment of orthopedic conditions.
The present invention generally relates to apparatus and methods for controlling forces at adjacent bone portions and/or constraining motion of the adjacent bone portions in one or more dimensions. More particularly, the present invention relates to a magnetic apparatus with at least two magnetic arrays each of which is constructed and implanted in a predetermined manner and generates interacting magnetic fields. Once implanted and secured to the adjacent bone portions, the apparatus provides interacting magnetic fields in the vicinity of the adjacent bone portions and is capable of transducing magnetic energy into mechanical energy and mechanical energy into potential magnetic energy, thereby reproducing functionally anatomic and or anatomically advantageous positions of the bone portions.
An apparatus for treating adjacent bone portions according to the invention includes first and second magnetic arrays. The first magnetic array is configured and dimensioned to be secured to a first adjacent bone portion and to provide a first magnetic field having first predetermined field characteristics and the second magnetic array is configured and dimensioned to be secured to a second adjacent bone portion and to provide a second magnetic field having second predetermined field characteristics. The first and second predetermined field characteristics are selected to interact such that the magnetic arrays cooperate to urge the adjacent bone portions into the predetermined desired relationship and constrain relative motion between the bone portions in at least two dimensions. Preferably, one or both magnetic array may comprise multiple magnets to provide a composite magnetic field, which may be symmetrical or asymmetrical. In one preferred embodiment, interaction between the first and second magnetic fields urges the arrays into a predetermined relationship with a defined reference point confined within a boundary defined by the magnetic field of one of the magnetic arrays.
According to a further aspect of the invention, the first predetermined field characteristics comprise magnetic equipotential surfaces or lines forming at least two first peaks defining a valley therebetween and the second predetermined field characteristics comprise magnetic equipotential surfaces or lines forming at least one second peak. Preferably, the peaks and valleys are three dimensional, for example at least two first peaks and valley therebetween being defined by a three dimensional, rotated sinusoid, and at least one second peak being defined by a three dimensional paraboloid. The first and second magnetic arrays are then positioned with respect to each other such that the second peak is received between the at least two first peaks. In other words, the field of one array preferably penetrates the field of the opposite array. In this embodiment the second peak is received within, e.g., the annulus of the toroid which may be topologically described as a cup-shaped region generated by rotating a sinusoid about its vertical axis. Alternatively, the first magnetic array is configured and dimensioned to provide the predetermined field characteristics with magnetic flux lines such that at least two peaks have different magnitudes.
In a further alternative embodiment, the apparatus according to the invention also comprises a first magnetic array and at least a second magnetic array. Further arrays may be provided. In this embodiment, the first array includes at least two magnets, configured and dimensioned to be secured to a first adjacent bone portion and to provide a first, composite magnetic field having first predetermined field characteristics such as magnetic flux lines defining at least one region of first magnetic intensity bounded by one or more regions of second magnetic intensity. The second magnetic array is configured and dimensioned to be secured to a second adjacent bone portion and to provide a second magnetic field having second predetermined field characteristics such as magnetic equipotential lines defining at least one region of third magnetic intensity. The regions of different magnetic intensity interact to urge the adjacent bone portions into the predetermined desired relationship and constrain relative motion between the bone portions in at least two dimensions. According to various alternatives, the regions of second and third magnetic intensity may have approximately the same magnetic intensity or the regions of second and third magnetic intensity may have different magnetic intensities and the regions of first and second magnetic intensity may have opposite polarities or the regions of first and second magnetic intensity may have the same polarity.
In a further alternative embodiment, the first and second magnetic arrays are secured to the adjacent bone portions at a predetermined distance apart along a first axis, and are oriented with respect to each other in a predetermined relationship along at least a second axis orthogonal to the first axis. The second magnetic array includes at least one magnet. At least two magnets of the first array and at least one magnet of the second array are arranged with common poles in opposition to produce a predetermined repulsive force therebetween at the predetermined distance. Relative movement between the arrays along the second axis away from the predetermined relationship is resisted by interaction between the magnetic fields in the regions of second and third intensity.
In a further aspect of the invention, each array has an opposing face and a back face, and comprises at least two magnets, each magnet having a polar axis. The magnets of each array are aligned with their polar axes substantially parallel such that the poles of each magnet are adjacent and disposed at the faces of each array. The arrays thus may be adapted to be secured to adjacent bone portions opposite to each other with the opposing faces facing together and in a predetermined positions with respect to each other along a first axis substantially parallel to the polar axes and along at least a second axis substantially orthogonal to the polar axes. In one alternative embodiment, the magnets of each array are aligned with opposite poles positioned on the opposing faces and the predetermined position along the first axis comprises the first and second array being at least substantially in contact along the opposing faces. In this embodiment, interaction between the magnetic fields resists relative rotation between the arrays. In another alternative, the magnets of each array are aligned with the same poles positioned on the opposing faces and the predetermined distance along the first axis comprises a predetermined spacing. In this alternative embodiment, interaction between the magnetic fields resists reduction of the predetermined spacing and resists movement away from the predetermined position along the second axis while permitting rotation thereabout or about other axes positioned adjacent to the second axis. Moreover, in this latter embodiment, at least one of the magnetic arrays may further comprise at least one magnet disposed in the array with an opposite pole positioned on the opposing face.
In a method for treating adjacent bone portions according to the invention, first and second magnetic arrays are secured to adjacent bone portions, each array being configured and dimensioned to provide a magnetic field having predetermined field characteristics. The arrays are positioned in a desired relationship. Relative motion of the adjacent bone portions is constrained in at least two dimensions, maintaining the desired relationship through interaction of the first and second magnetic fields. An alternative method according to the invention involves securing a first magnetic array to a first adjacent bone portion to provide a first composite magnetic field therearound, securing a second magnetic array to a second adjacent bone portion to provide a second composite magnetic field therearound, and disposing the first and second magnetic arrays in opposition to each other to simultaneously generate both repulsive and attractive force therebetween, thereby urging the adjacent bone portions into a predetermined desired relationship and constraining relative motion of the adjacent bone portions in at least two dimensions. In a further aspect of the invention, the first and second adjacent bone portions form opposing bone portions of an articular joint and wherein the magnetic fields interact to reduce the joint reactive forces while constraining the bone portions to move in a natural joint motion. In an alternative aspect of the invention, the first and second adjacent bone portions are opposite sides of a bone fracture and the magnetic fields interact to reduce and stabilize the fracture fragments.
According to further aspects of the invention, a magnetic array may be constructed by arranging one or more magnets or arranging the poles of the magnets (both collectively referred to as xe2x80x9cmagnetsxe2x80x9d hereinafter) in a predetermined configuration and/or orientation. Due to the coincidence of the magnetic fields of individual adjacent magnets, the magnetic array creates a composite magnetic field which is capable of exerting two- or three-dimensional magnetic force upon objects disposed nearby. By manipulating properties, shapes, and other characteristics of each magnet and by arranging them in a predetermined configuration and/or orientation, the magnetic arrays and their interaction can be utilized to control forces between the adjacent objects and/or constrain their motion in two or three dimensions including rotation.
In another aspect of the invention, the magnets of the magnetic array may be secured into a housing, while maintaining the configuration and/or orientation thereof. By providing prearranged configuration and/or orientation thereto, the magnetic array can be readily adapted to treat variety of orthopedic conditions. This arrangement avoids potentially unpredictable implantation of individual magnets into different locations in the adjacent bone portions, simplifies the implantation procedure, reduces the time of the surgical procedure, minimizes complications following the surgery, facilitates the healing process, and provides a treatment option that is easier to perform and can be performed in a competent fashion by a greater number of surgeons.
In yet another aspect of the invention, the magnetic arrays are implanted into adjacent bone portions so as to control forces at the adjacent bone portions and/or to constrain the motion of adjacent bone portions in one or more dimensions. When one magnetic array is disposed in an opposed relationship to another magnetic array, the composite magnetic fields of each of the magnetic arrays interact with each other, and generate dynamically interacting magnetic fields between and/or around those magnetic arrays. Characteristics of the interacting magnetic fields can be specifically controlled by manipulating properties, shapes, and/or other characteristics of each individual magnet in each magnetic array, because the resultant of the interacting magnetic fields is a vector sum of the individual composite magnetic fields of each magnetic array. By manipulating the repulsive and/or attractive forces generated therebetween, the magnetic arrays can provide potential energy to do work along the axis parallel and orthogonal to the direction of the magnetic polarity, as well as provide rotational stability for particular array designs to the adjacent bone portions. This potential energy can be used to reduce the reactive force between the bone portions, and/or limit motion between the bone portions. According to the invention, the orthopedic magnetic apparatus including the foregoing magnetic arrays may be applied to various orthopedic conditions such as long bone fractures, carpal bone fractures, joint instability, early arthritis and end stage arthritis. They may also be used to augment the designs of other total joint components. In treating fractures, the magnetic arrays of the invention may be arranged to create dominant attractive force, thereby providing the structural and/or rotational stability thereto.
As indicated, in one aspect of orthopedic application of the present invention, the magnetic arrays described herein above may be applied to treat degenerative conditions such as arthritis. For such degenerative conditions, the magnetic arrays may preferably be arranged to create dominant repulsive force, thereby providing potential magnetic energy to counteract mechanical forces along the axis parallel to composite magnetic force vector and provide stability along the axis orthogonal to the composite magnetic force vector. Benefits may be realized in reducing mechanical contact between the intact cartilage of the bone portions at a joint by reducing the joint reactive force and providing the additional means of control to diminish joint instability and/or the progression of joint disease. Moreover, the invention may be employed in or with prostheses to reduce the mechanical contact and the damage caused by friction between implanted prosthetic components, reducing joint reactive force, and providing the stabilizing capability, thereby decreasing pain associated with the end-stage arthritis and/or extending the functional life of the implanted components.
The term xe2x80x9cadjacent bone portionsxe2x80x9d generally refers to any bones or portions thereof which are disposed adjacent to each other. The xe2x80x9cadjacent bone portionsxe2x80x9d or simply the xe2x80x9cbone portionsxe2x80x9d may mean any bones or their portions positioned adjacent to each other, whether they are separate or functionally coupled with each other, and/or mechanically contacting each other due to anatomical reasons, non anatomic reasons and/or surgical treatments. For example, a tibia and fibula, a radius and ulna, and a femur, tibia, and fibula are a few representative pairs or groups of the bones anatomically disposed adjacent to each other; a femur and tibia, a humerus and ulna, and a humerus and scapula are exemplary bone pairs functionally coupled to each other through a knee joint, elbow joint, and shoulder joint, respectively; and a clavicle and sternum are the bones mechanically contacting each other. The xe2x80x9cadjacent bone portionsxe2x80x9d may also include any two or more bone segments which are to be positioned adjacent to each other, and/or contacting each other. Examples of such bones may include any number of fractured segments of a bone(s) and/or joint(s).
The terms xe2x80x9cequi-potential linexe2x80x9d and xe2x80x9cequi-potential surfacexe2x80x9d mean, respectively, any curvilinear two-dimensional line and three-dimensional surface, representing characteristics of a magnetic field generated around a magnet(s). The xe2x80x9cequipotential surfacexe2x80x9d is perpendicular to magnetic fluxes emanating from the magnet and is drawn by connecting points of the same magnetic intensity on the magnetic fluxes. The xe2x80x9cequipotential linexe2x80x9d is obtained by taking a cross-section of the xe2x80x9cequipotential surfacexe2x80x9d in a predetermined direction. Thus, the xe2x80x9cequipotential linexe2x80x9d is a subset of xe2x80x9cequipotential surfacexe2x80x9d and also perpendicular to the magnetic fluxes in the predetermined direction. For ease of illustration and simplicity, both xe2x80x9cequipotential linexe2x80x9d and xe2x80x9cequipotential surfacexe2x80x9d will be collectively referred to as xe2x80x9cequipotential linexe2x80x9d hereinafter. Accordingly, xe2x80x9cpeaks,xe2x80x9d xe2x80x9cvalleys,xe2x80x9d and xe2x80x9cgapsxe2x80x9d of the xe2x80x9cequipotential linesxe2x80x9d are inclusive of those depicted in the two-dimensional xe2x80x9cequipotential linesxe2x80x9d as well as those in the three-dimensional xe2x80x9cequipotential surfaces.xe2x80x9d